1. Field of the Invention
This invention relates to an apparatus for needling a nonwoven web, which apparatus comprises at least one needle beam carrying a needle board, a rocker for guiding the needle beam, and a slider-crank mechanism for actuating the needle beam.
2. Description of the Prior Art
Needle beams which carry needle boards are actuated in general by slider-crank mechanisms, which are either connected to the needle beams by means of push rods in sliding contact with guides or which are pivoted to rockers, which carry the needle beams (Austrian Patent Specification 249,392). The guiding of the needle beam by means of a rocker affords the advantage that the structure is simple because gush rods and associated guides are no longer required between the connecting rods of the slider-crank mechanisms and the rockers. But a simple guidance by a rocker will cause the needles to move along an arc of a circle and although the 1ever length of the rocker is large relative to the amplitude of oscillation this may influence the needling effect so that the non-woven web is more effectively felted than when the needles are guided along a straight path. It must be taken into account, however, that the depth of penetration will vary in dependence on the distance from the pivotal axis of the rocker in the direction of travel of the nonwoven web.
Regardless of whether the needles are guided along a straight path or by a rocker, the use of slider-crank mechanisms for reciprocating the needle board will give rise to vibration problems. If slider-crank mechanisms are used to actuate needle beams which are guided along a straight line by means of push rods, it is known to balance the first-order mass forces and mass moments in that the slider-crank mechanism is provided with two parallel crankshafts or eccentric shafts, which can be driven to rotate in mutually opposite senses and are connected by connecting rods to a common link, which is connected to the push rods. But such means for mass balancing cannot readily be used with a rocker for guiding needle boards because the movement of the needle board along an arc of a circle will give rise to considerable transverse vibrations if the slider-crank mechanism is conventionally arranged.